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Battery Battle

Thursday, 08 October 2009

A new type of redox flow battery from the Fraunhofer Institute for Chemical Technology (ICT) offers an advantage for electric cars. If the rechargeable batteries are low, the discharged electrolyte fluid can simply be exchanged at the gas station for recharged fluid – as easy as refilling the gas tank.

The German government plans for one million electric cars to be sold in Germany by the year 2020. Until then, researchers still have to overcome hurdles like the question of energy storage. Lithium-ion batteries are a possible solution, but they still take hours to charge.

The ICT researchers see an alternative in redox flow batteries. “These batteries are based on fluid electrolytes. They can therefore be recharged at the gas station in a few minutes – the discharged electrolyte is simply pumped out and replaced with recharged fluid,” says engineer Jens Noack. “The pumped-off electrolyte can be recharged at the gas station, for example, using a wind turbine or solar plant.”

The principle of redox flow batteries is not new. Two fluid electrolytes containing metal ions flow through porous graphite felt electrodes, separated by a membrane, which allows protons to pass through it. During this exchange of charge a current flows over the electrodes, which can be used by a battery-powered device.

Until now, however, redox flow batteries have had the disadvantage of storing significantly less energy than lithium-ion batteries. The vehicles would only be able to cover about a quarter of the normal distance – around 25 kilometers – which means the driver would have to recharge the batteries four times as often.

“We can now increase the mileage four or fivefold, to approximately that of lithium-ion batteries,” Noack says. The researchers have produced the prototype of a cell, and now they must assemble several cells into a battery and optimize them. The research team is testing electric drives and energy storage units on model vehicles that are about a tenth of the size of normal vehicles.

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